Quick and dirty code to fit emperical forcefield nonbonded parameters to ab initio single points.

git clone https://github.com/aehogan/ffit.git
cd ffit
mkdir build
cd build
cmake ..
make

cd ffit/examples
../build/ffit he.inp

See examples/co2.data or examples/he.data for the format of ab initio input data. Briefly, the data files are modified XYZ format files with the ab initio energy in K/kB on the comment line and a molecule id number added before the XYZ data and an atomic charge added after.

• Lines starting with ! or # are treated as comments
• steps [int]
  • number of fitting steps, can be zero to only print out information of the current fit
• output_freq [int]
  • after how many steps to print fitting information
• max_energy [float]
  • the energy scaling parameter to start reducing the important of very repulsive configurations
• data_file [str]
  • filename for an ab initio data file
• es [on|off]
  • permanent electrostatics on / off
• pol [on|off]
  • induced dipole electrostatics on / off
• lj [on|off]
  • Lennard-Jones potential on / off
• phahst [on|off]
  • modified tang toennies (exponential 6-8-10) on / off
• type_map [str] [int]
  • atom name to atom id
• lj_sig [int] [float]
  • atom id and initial Lennard-Jones sigma (or exponential rho) in angstrom
• lj_eps [int] [float]
  • atom id and initial Lennard-Jones epsilon (or exponential beta) in K/kB (or angstrom^-1)
• c6 [int] [float]
  • atom id and initial c6 in a.u.
• c8 [int] [float]
  • atom id and initial c8 in a.u.
• c10 [int] [float]
  • atom id and initial c10 in a.u.
• alpha [int] [float]
  • atom id and initial polarizability in angstrom^3